Screw



Dec. 8, 1942. 'r. A. OLEARY 2,304,704

SCREW Filed Dec. 4, 1939 2 Sheets-Sheet 1 INVEINIZCR, ffizaoaxe 4.01542) BY xi/M ATTORNEY.

Patented Dec. 8, 1942 SCREW Theodor A. OLeary, New York,

N. Y., assignor of forty-eight and one-third per cent to Winslow Foster,New York, N. Y. I

Application December 4, 1939, Serial No. 307,504

curved lower wall of the slot these side walls become progressivelyshorter vertically as they ap- 9 Claims.

This invention relates to new and useful improvements in screws adaptedto be driven into wood, metal or other materials and relates moreparticularly to an improved type of slot in the head of a screw, suchscrew being adapted to be driven by a special type of driver. Thepresent application constitutes a continuation-in-part of my co-pendingapplication Serial No. 75,611, Screws and the method of making same(since issued as Patent No. 2,182,092, December 5, 1939) such latterapplication having been a division of my earlier application Serial No.61,931, Screws and driver means therefor.

It is well known that considerable difliculty is always experienced inretaining the bit portion of a screw driver in the screw slot during thedriving operation. Various expedients hav been devised to provide somepositive connection between the bit of the driver and the head of thescrew which will prevent ateral displacement of the former relative tothe latter and will also prevent the bit from jumping out of the slot,particularly in cases wherein the screw is cuttin the hole in thefirstinstance. Most of the efforts to solve the problem have beenunsatisfactory for the reason that no cooperating structures weredevised to maintain a proper balance of rigidity and flexibility betweenthe driving and driven elements.

Screws have been provided with special slots which are dove-tailed intransverse section, the screw driver having flanges on either side ofthe bit which engage the sides of the dove-tailed or undercut slot. Inthe case of flat headed screws, however, which are adapted to becounter-sunk flush with the surface of the member in which the screw isdriven, it is impossible to remove the bit of such screw driver afterthe screw has been driven home.

It is one of the principal objects of the present invention to provide ascrew having a slot of particular formation, adapted to be driven with aspecially formed driver, such slot having a lower wall which isconcavely curved through substantially its entire length, such slotpreferably terminating at each end thereof just short of the peripheryof the screw head in the case of the flat headed screw. The opposed sidewalls of the slot are not vertical nor parallel with each other, as inthe case of the conventional screw slot, but rather are inwardlyinclined at their central portions and progressively cal and parallelwith each their terminals.

It will also be appreciated that in view of the other as they approachbecome more nearly vertiproach such terminals. Thus it will be apparentthat the opposed upper edges of the slot are slightly convexly curvedthroughout all or substantially the greater portion of their length.

This screw, with its undercut or dove-tail slot, is adapted to be drivenby a driver preferably having some degree of curvature along the loweredge of the bit portion, such bit portion havin opposed flanged wallsadapted to be received in the undercut screw slot from the side thereof.When so positioned therein, longitudinal displacement of the bitrelative to the slot is prevented and if means are carried on the bitfor yieldingly or otherwise engaging the head of the screw head, lateraldisplacement of the bit during the driving operation is prevented aswell. A particularly effective driver for driving the screw of suchcharacter and comprising a split bit structure, the bit portionsentering and leaving the slot from each end thereof, is described in aco-pending applicafion.

The precise curvature of the lower wall of the slot, as well as itslength relative to the diameter of the screw head, is a matter ofchoice. Likewise, the particular curvature of the side walls of the slotcan be varied within limits without departing from the spirit of theinvention.

This slot may be formed in a variety of ways, although the methoddescribed in my co-pending application Serial No. 75,611, which includesthe steps of forming a slot with substantially parallel walls and thenupsetting the head by a suitable die to cause the central portions ofsuch side walls to converge, is the most preferable.

Another object of the present invention is the provision of another ingsuch slots, as well as for forming conventional slots in screw heads.For countless years a slot has been formed in the head of a screw bycutting the slot in the otherwise finished head by means of a circularmilling cutter. This method is relatively expensive and production isdistinctly limited because of the well defined limitations on the' speedof this cutting element. In other words, a considerable number of slotcutters are required to cut the slots in screws produced by a singlehead forming and thread cutting machine.

My co-pending application Ser. No. 75,611 related to a method of forminga special type of undercut or dovetail slot in a screw head by anupsetting process. Essentially, this method comprised the steps ofplacing the wire in a supporting die, striking the head portion topartially improved method for formform or cone-up the head, thenstriking the head portion with a combined head forming and slot formingdie which formed the transverse .slot, the die being so shaped as toleave a slight excess of material in the central portion of the head.The final operation was to strike the head, while still supported in thesamedie, with an upsetting die which, in the case of a flat head in ascrew head by upsetting means diifers in certain essential respectsfromthat described in my earlier application and may be employed forforming a slot of the type Just described or for forming a conventionalscrew slot.

Struck-in screw slots have been previously unsatisfactory in the pastfor the reason that such slot was not a true rectangle or square intransverse section for the reason that if the slot forming die were soshaped as to form such a-slot, it could not be removed. In other words,if the opposed walls of such a die were parallel the flowing metal wouldtravel in such a fashion as to effectivelyweldthe die in the slot.Conversely, if the die were given a more nearly V-shaped formation, theslot was unsatisfactory because the driver would not remain thereinduring the driving operation, and, more particularly, the opposed upperedges of the slot were not square or sharp but were rounded, therebymaking the screw unfit for ordinary use.

It is accordingly one of the objects of the present invention to providea method of striking a slot in the head of the screw either as part ofthe head forming operation or as a separate step after the head has beenformed, the method also including a novel step for straightening up theside walls of the slot to make them conform to through a flat headedscrew formed in accordance with the present invention;

Fig. 2 is a similar section taken on line 2-4 of Fig. 1;

Fig. 3 is a vertical section taken on line 3-3 of Fig. l;

Fig. 4 is a top plan view of the fiat headed screw;

Fig. 5 is acentral vertical section taken through a round headed screwconstructed in accordance with the present invention;

Fig. 6 is a central vertical section taken on line G6 of Fig. 5;

Figzfl is a top plan view of such screw;

Fig. 8 illustrates the cooperating dies used to form a fia't headedscrew from a previously conedup blank;

Fig. 9 illustrates the die supporting the formed employed for strikingin the and the finished, slotted head;

the slot formed by a milling cutter or to cause the central portionsthereof to converge inwardly, as in the case of my improved screwpreviously described, which is adapted to be driven with a specialdriver.

In the preferred method of carrying out my invention, one of the stepsis to strike the blank,-

which may or may not, as desired, be previously partially formed orconed-up. with a combined head forming and slot forming die. It isclearly within the scope of my invention, however, to

first form the head by upsetting or otherwise, and

then to strike in the slot. The die for so forming the slot has opposedwalls which are shaped as to form an initial slot with non-parallelwalls, the opposed walls at their lower ends being closer together thanat their upper ends. This die also leaves excess material preferablyalong the entire length of the slot and when the head is struck thefinal blow, these non-parallel walls are in efiect straightened up to apoint wherein they are substantially parallel with each other. the upperedges of such walls likewise being relatively sharp and not rounded.

In the drawings:

Fig-Q1 is a central vertical section taken Fig. 13 is a top plan view ofthe finished screw;

Fig. 11 shows a lower or stationary die similar to-that shown in Fig. 8,such die supporting a previously coned-up blank and further shows amovable die which is adapted to both form the head and strike in theslot;

Fig. 15 shows the upper die having been moved into engagement with thestationary die and having formed the head and slot;

Fig. 16 shows the finished slotted head after the same has been struckwith the final die;

Fig. 17 shows a modified form of operation wherein the relation of theinitial die is such as to leave excess material over the entire uppersurface of the head when the slot is struck in; Fig. 18 shows thecompletely formed head after ithas been struck with the final die;

Fig. 19 is a top plan view of the finished screw with the centraldovetail portion;

Fig. 20 is a section on line 2020 of Fig. 19;

Fig. 21 is a section taken on line 2l-2l of Fig. 19;

Fig. 22 is a section taken on line 22-22 of Fig. 19;

Fig. 23 is'a broken section taken through upper; die 63 (Fig. 15) buttaken at one side of the center thereof.

The screw comprising the present invention includes a conventionaltapered shank portion I0 provided with conventional threads II, a headportion l2 being formed at the upper end of the screw which in Figs. 1to 4, inclusive, is a fiat head. The screw head is formed with'atransverse recess comprising a lower wall 14 which is concavely curvedthroughout its length, such slot terminating at each end thereof at apoint I 8 which is just short of the periphery l5 of the screw asillustrated at I6. This lower wall I4 is of substantially the same widththroughout its length and in the central portion of the slot the opposedside walls l8 converge inwardly as illustrated in Fig. 2, thus forming adovetail portion to receive the flanged bit previously mentioned. Asthese side walls approach their terminals, they become progressivelymore nearly parallel to each other, as indicated at l8 in Fig. 3. Theupper surface 20 of the head 12 is in any other type of screw,

thus formed with opposed, convexly curved edges 2| such screw slot.

The screw shown in Figs. 5, 6 and 7 is a round headed-machine screw witha shank 24 having a threaded portion 25, the round head being indi-Whereas a flat headed screw and a round head screw have been chosen forillustration of the present invention, it will be neverthelessappreciated that this type of slot maybe made such as one with afilister head, button head, or otherwise. It will further be appreciatedthat the invention may be applied to a screw of any size and also to awood screw of the type shown in Figs. 1 to 4 of a machine screw of thetype shown in Figs. 5 to 7, or to any other type of screw adapted toeither cut its own threads or to be driven into a previously threadedaperture.

The hereindescribed method of forming a slot in the head of a screw maybe adopted for forming conventional slots of the type which has beenused since time immemorial or it may be employed for making slots of thespecial type disclosed in this and in my earlier application.

Figs. 8 to 13, inclusive, illustrate the method as applied to aconventional screw and in carrying out the method a substantiallycylindrical stationary die 3| having a central aperture 32 thereinreceives a screw blank 33, which is formed with a previously coned-uphead portion 34. The precise shape of this coned-up portion is dependentupon the shape and size of the head to be subsequently formed, a will beappreciated by those skilled in the art. The coning-up step is notessential in carrying out the present method, although it is desirablesince it is a simple oper ation and reduces the wear on the headingpunch or die. The aperture 32 is formed at its upper end with a taperedportion 36 corresponding to the shape of the lower surface of the screwhead to be formed. The movable die 39 in the case of the flat headedscrew has a flat lower surface 40 which forms the fiat head portion 42,shown in Fig. 9. The movable die 44 is formed as shown in Fig. 9 andincludes a male portion 45, having non-parallel side walls 46 and arecessed portion 41. After this die has struck the 5;

head portion 42, it forms the slot 49 shown in Fig. 10, the upper edges50 of the slot throughout their length at this stage of the operationbeing raised slightly above the upper surface of the stationary die 3|.

This head portion is now struck with a die 52 which has a flat lowersurface similar to the die 39, and such die causes the opposed sidewalls of the slot to become straightened, as indicated at 54 in Fig. 12.The lower wall 56 of this slot throughout the operation is fiat, asshown in Fig. 11, and the extent to which the upper edge 50 of the sidewalls of the slot prior to the final blow is moved, is dependent uponthe shape and size of the screw head to be formed. The head 5'! of thefinished screw shown in Fig. 13 is thus similar to a conventional screwhead having the usual transverse slot 58. If the lower edges of the slotare slightly rounded as a result of the formation of male portion 45,this final blow also position as shown causesthe edges to become squareas shown Fig. 12.

Substantially the same method of forming the slot is shown in Figs. 14to 16, although the slot in this instance is of the type disclosed inFigs. 19 'to 22, namely, the dovetail slot of the special type disclosedherein and the initial slot as well as the head are both formed in oneoperation. In this instance the stationary die 60 likewise receives theconed-up blank 6| in a central aperture 62. .The movable die 63 isformed with a male portion 64 and recessed portions 65, but in thisinstance the shape of the movable die is so formed that when the finaldie 66, which in this instance is fiat, strikes the head portion thecentral portions of the walls are caused to converge and the terminalportions are caused to be straightened. In other words, the die 63 isspecially formed for each type of screw slot to be formed. In my Iearlier application relative to the method of making such a screw, Ileft excess material only in the central portion of the head prior tothe final blow. In accordance with the present invention, however, thereis no limitation as to where this excess material is to be left and itmay be formed over the entire head of the screw. It will accordingly beapparent that the male portion 64 of die 63 is not of the same crosssectional formation throughout its length; For

illustrative purposes, it may be stated that this male portion in itscenter is of' the shape shown in Fig. 15 but as it approaches itsterminals it becomes more shallow as shown in Fig. 23 and the opposedwalls 68 at this portion are more angular relative to each other.Accordingly, when this die strikes the head portion the slot so formedhas walls which are more nearly parallel with each other at the centerthan at the ends. Thus when the head 69 is struck with the final die,such as die 66 in the case of the flat headed screw, these centralportions converge inwardly, as shown at 10 in Fig. 21, and the terminalportions which are more shallow are merely straightened to assume a morenearly parallel at H in Fig. 22.

- In Figs. 17 and 18, the head portion 14 of the screw 15, supported indie 16, is struck with die 11 having a male portion 18 and a circularrecessed portion 19, thus leaving excess material over the entire areaof this head portion as shown at80. The flat die 8| striking the headcauses all of the material in the upper head portion to flow, thusforming slot 82 in the finished head.

Thus, two general means of carrying out the method are illustratedherein, to wit, that illustrated in Figs. 11 and 12 and that illustratedin Figs. 17 and 18. In the former, the excess material is left adjacentto the slot over the full length thereof and in the latter the excessmaterial is left over the entire head of the screw. It will beappreciated that this process may be varied considerably withoutdeparting from the spirit of the invention.

The complete mechanism for carrying out the method is not disclosedherein since a two or three blow header is well known in the art andprovides means for shifting the dies after they have done their work.

What I claim is:

1. A screw provided with a head having an undercut transverse slot inthe upper surface thereof, the slot being curved along its lowersurface.

2. A screw provided with a head having a transverse slot in the uppersurface thereof, the slot having inwardly converging side edges andbeing curved along its lower edge, the opposed terminals of the slotbeing spaced from the periphery of the head.

3. A screw provided with a head having a transverse slot therein, thelower surface of the slot being curved and being of substantiallyuniform width, the side walls of the slot converging inwardly.

4. A screw provided with a head having a transverse slot therein, thelower surface of the slot being curved and being of substantiallyuniform width, the side walls of the slot being inwardly converging, thescrew being capable of being driven by a driver provided with a bitportion, the opposed surfaces of which are non-parallel and are of suchdimensions as to fit the transverse slot in the head of the screw.

5. A screw formed with a head having a trans-- verse slot therein, suchslot being formed with a concavely curved lower wall of substantiallyuniform width throughout its length, the opposed side walls being soformed as to converge inwardly at the central portion thereof, suchwalls, as they approach their terminals, becoming progressively morenearly parallel with each other.

6. A screw provided with a head portion having a transverse slot thereindefined by a lower wall and opposed side walls, the lower wall beingcon-.

cavely curved and being of substantially the same width throughout itslength, the central portions of such side walls converging inwardly toform a dovetail effect, the terminal portions of the opposed walls beingsubstantially parallel with each other.

7. A screw provided with a head portion having a transverse slot thereindefined by a lower wall and opposed side walls, the lower wall beingconcavely curved and being-of substantially the same width throughoutits length, the terminal portions of the opposed walls beingsubstantially parallel with each other, the central portions ofsuch sidewalls converging inwardly to form anundercut portion adapted to receivea screw. driver having a flanged bit portion and thus preventlongitudinal displacement of the screw relative to the driver during thedrivingoperatiom 8. A screw formed with a head having a transverse slottherein, the opposed upper edges of the slot being convexly curvedthroughout their length, the lower wall of the slot being ofsubstantially uniform width, and being concavely curved, throughout .itslength, the opposed side walls of the slot'being substantially parallel'adjacent to-their end sections and inwardly converging midway betweentheir end sections to form a central dovetail section, the opposed wallportions between the central dovetail section and the end sections beingformed progressively more nearly parallel to each other.

9. A screw formed with a head having a transverse slot therein, thelower wall of the slot being concavely curved throughout its length andbeing of substantially uniform width throughout its length, the opposedside walls of the slot converging inwardly at their upper centralportions, said side walls becoming progressively more nearly parallelwith each other as they approach their terminals and being substantiallyparallel with each other at their terminal portions.

1 THEODOR A. OLEARY.

